Revert "os/exec: avoid calling LookPath in cmd.Start for resolved paths"
This reverts CL 512155.
Reason for revert: CL 512155 introduced a race in that it caused
cmd.Start to set cmd.Path. Previously it was fine if code looked
at cmd.Path in one goroutine while calling cmd.Start in a different
goroutine.
A test case for this race is in CL 527495.
Change-Id: Ic18fdadf6763727f8ea748280d5f0e601b9bf374
Reviewed-on: https://go-review.googlesource.com/c/go/+/527337
Auto-Submit: Ian Lance Taylor <iant@golang.org> Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Matthew Dempsky <mdempsky@google.com>